[Help] File changes do not remain after reboot.

So I'm new to the M8, and today I rooted and unlocked the bootloader. I wanted to change the HTC emoji to the default Kitkat ones, which requires just deleting or renaming a file in the fonts folder, located in /system.

I can make the change, but when I reboot, it reverts the changes and restores the previous file that I removed.

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